The south west main railway line near Dawlish. Photograph: Hazel Strange

The railway line west of Exeter along the South Devon coast provides arguably the most beautiful rail journey in the UK. It is also one of the most expensive to maintain and its vulnerability was illustrated recently by the destruction of the route at Dawlish during February’s storms. It reopens today, but few people who travel on the line nowadays realise that this was once the site of an ambitious experiment in railway propulsion that could have changed railway history.

The Great Western Railway looks west from Exeter

When the railway from London and Bristol reached Exeter in 1844 there was pressure to extend west towards Plymouth. Isambard Kingdom Brunel was the chief engineer of the Great Western Railway and, committed to technological innovation, he was attracted to a new means of motive power for the extension. He had visited Dalkey in Ireland in 1843 where a short but steep section of railway was driven by “atmospheric power” and, impressed by what he had seen, was keen to try the same on the much longer South Devon Railway. He had also been concerned about the ability of contemporary locomotives to cope with the gradients west of Exeter. The coastal route via Dawlish was a partial solution but although it avoided hills, it left the track vulnerable to storms as we know to our cost. Further west, hills are unavoidable and Brunel thought that atmospheric power would cope better than locomotives.

The science of atmospheric power

In this system, a piston (attached to the train) is contained in a large metal tube laid between the tracks. The tube is evacuated ahead of the train by a series of engine houses (with steam-driven pumps) situated roughly every three miles along the route. Atmospheric pressure acting on the piston provides the motive force, pushing the train forwards. This is similar to the principle used in early Newcomen-type steam engines. This system does away with the need for a mobile power plant in the form of a locomotive thus reducing the weight of the train. Brunel argued that this provided considerable economic advantage.

The biggest problem the atmospheric system faced was maintaining the vacuum while the piston moved. In the Clegg and Samuda design, adopted by Brunel, a slit along the top of the metal tube accommodates the piston and a hinged leather flap seals the slit maintaining the vacuum. As the train moves, the leather flap lifts ahead of the piston and, once the train has passed, the flap seals again. The original design included a protective weather seal which Brunel ignored; this was probably false economy given the effects of Devon rain and sea air.

The atmospheric railway works, for a while

One of the surviving atmospheric engine houses. This one was built at Totnes station to extend the Atmospheric Railway towards Plymouth but was never commissioned. Photograph: Hazel Strange

Construction of the engine houses was delayed so that, when the coastal line between Exeter and Newton Abbot via Dawlish opened in 1846, locomotives were used. By 1847 the atmospheric infrastructure was in place and testing began followed by limited public services from September of that year. A full timetable worked by atmospheric trains was introduced over the 20 mile section between Exeter and Newton Abbot early in 1848 and worked quite well on many days once the winter was over, with trains travelling at speeds up to 70 mph.

The system, however, experienced recurrent difficulties and working costs were higher than expected. By far the worst problem was the leather flap which degraded under working conditions losing its seal and eventually tearing, despite attempts at lubrication. Loss of vacuum meant that train services were disrupted and coal costs soared as pumps worked overtime to maintain vacuum against leaks. Eventually a complete and costly replacement of the leather seals was needed. By September Brunel recommended that atmospheric power should be abandoned and after less than a year the line reverted to locomotive working.

The aftermath of the atmospheric experiment

Brunel was criticised for championing a system that ultimately had to be abandoned, but the atmospheric railway should not be seen as a complete failure. Although from our 21st century perspective the atmospheric system might seem cumbersome, to early Victorian railway engineers it was a real alternative to locomotive power. Indeed, for a short time it provided a service as fast and as punctual as a locomotive-driven railway. There was also great public enthusiasm for the system which was known colloquially as “Brunel’s atmospheric caper”. Despite this, atmospheric power quickly lost any advantage it had, partly because of its inherent problems but also because of rapid advances in locomotive technology.

Atmospheric power has not been forgotten, and in 2013 an atmospheric people-mover began operation at an airport in Brazil. The name also lives on in Totnes where a proposed community business park based near the old engine house has been named the ATMOS project.